Thermal inkjet hardcopy devices such as printers, graphics plotters, facsimile machines and copiers have gained wide acceptance. These hardcopy devices are described by W. J. Lloyd and H. T. Taub in "Ink Jet Devices," Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. The basics of this technology are further disclosed in various articles in several editions of the Hewlett-Packard Journal [Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 February 1994)], incorporated herein by reference. Inlet hardcopy devices produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes the paper.
An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes "dot locations", "dot positions", or pixels". Thus, the printing operation can be viewed as the filing of a pattern of dot locations with dots of ink.
Inkjet hardcopy devices print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
The typical inkjet printhead (i.e., the silicon substrate, structures built on the substrate, and connections to the substrate) uses liquid ink (i.e., dissolved colorants or pigments dispersed in a solvent). It has an array of precisely formed orifices or nozzles attached to a printhead substrate that incorporates an array of ink ejection chambers which receive liquid ink from the ink reservoir. Each chamber is located opposite the nozzle so ink can collect between it and the nozzle. The ejection of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements. When electric printing pulses heat the inkjet firing chamber resistor, a small portion of the ink next to it vaporizes and ejects a drop of ink from the printhead. Properly arranged nozzles form a dot matrix pattern. Properly sequencing the operation of each nozzle causes characters or images to be printed upon the paper as the printhead moves past the paper.
The ink cartridge containing the nozzles is moved repeatedly across the width of the medium to be printed upon. At each of a designated number of increments of this movement across the medium, each of the nozzles is caused either to eject ink or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed movement across the medium can print a swath approximately as wide as the number of nozzles arranged in a column of the ink cartridge multiplied times the distance between nozzle centers. After each such completed movement or swath the medium is moved forward the width of the swath, and the ink cartridge begins the next swath. By proper selection and timing of the signals, the desired print is obtained on the medium.
A concern with inkjet printing is the sufficiency of ink flow to the paper or other print media. Print quality is a function of ink flow through the printhead. Too little ink on the paper or other media to be printed upon produces faded and hard-to-read documents.
In an inkjet printhead ink is fed from an ink reservoir integral to the printhead or an "off-axis" ink reservoir which feeds ink to the printhead via tubes connecting the printhead and reservoir. Ink is then fed to the various vaporization chambers either through an elongated hole formed in the center of the bottom of the substrate, "center feed", or around the outer edges of the substrate, "edge feed". In center feed the ink then flows through a central slot in the substrate into a central manifold area formed in a barrier layer between the substrate and a nozzle member, then into a plurality of ink channels, and finally into the various vaporization chambers. In edge feed ink from the ink reservoir flows around the outer edges of the substrate into the ink channels and finally into the vaporization chambers. In either center feed or edge feed, the flow path from the ink reservoir and the manifold inherently provides restrictions on ink flow to the firing chambers.
Air and other gas bubbles and particulate matter can cause major problems in ink delivery systems. Ink delivery systems are capable of releasing gasses and generating bubbles, thereby causing systems to get clogged and degraded by bubbles. In the design of a good ink delivery system, it is important that techniques for eliminating or reducing bubble problems be considered.
Inkjet printheads are typically attached to a housing or body pf a print cartridge which contains an ink reservoir. The housing has a conduit for supplying ink from the ink reservoir to the printhead. Inkjet printheads are very sensitive to particulate contamination. To deal with this problem, a filter is typically disposed between the reservoir of ink and the printhead. A filter is attached to the inside of the housing, separating the ink conduit of the housing into two regions--one upstream and one downstream of the filter. This type of design has a number of drawbacks.
First, the housing material tends to be selected for structural rigidity and high heat deflection. Fillers (such as glass fibers) are typically included to enhance these properties. Such materials tend to be difficult surfaces to which to attach a filter and effect a complete seal around the perimeter of the filter. If the seal is not complete, bubbles or particulates may slip past the filter and block the ink channels or nozzles.
One method to improve upon this is to provide a second plastic material by insert molding to rigid outer housing. However insert molding is very expensive and the outer rigid housing must be adapted to be compatible with insert molding. The separation the filter staking from the cartridge housing would provide more freedom of material selection for both the cartridge housing and a good heat staking material for the filter carrier. Moreover, the filter staking process is greatly simplified when it can be performed external to the cartridge housing is done outside a pen body. All of these difficulties are even further compounded by the advent of a new design that provides a jet impinging flow of ink to cool the printhead. This design makes the molding of the rigid housing very difficult.
Another problem that occurs during the life of the print element is air out gassing. Air builds up between the filter and the printhead during operation of the printhead. For printers that have a high use model, it would be preferable to have a larger volume between the filter and the printhead for the storage of air. For low use rate printers, this volume would be reduced.
Accordingly, there is a need to provide a way to reduce dependency of the filter attach properties upon the selection of exterior housing properties without adding a costly insertion molding process. Further, there is a need to provide a housing and filter design that makes the jet impinging flow design easier to mold. There is also a need for a way to provide a variable volume for the storage of out gassed air for the same print cartridge housing.